A large capacity electrolytic capacitor having a low equivalent series resistance (hereinafter referred to as “ESR”) in a high frequency region has been required in the area of electrolytic capacitors as electronic components in response to the frequency increase of electronic apparatuses.
Recently, for reducing ESR in the high frequency region, the solid electrolytic capacitor (hereinafter referred to as “SEC”) employing solid electrolyte made of conductive polymer molecules or the like having high electric conductivity has been studied. For increasing the capacity, a SEC is commercialized that is formed by filling conductive polymer molecules into a winding capacitor element where a separator is disposed between anode foil and cathode foil and wound.
For preventing contact between anode foil and cathode foil, the winding SEC requires a separator to be disposed between anode foil and cathode foil. This separator is made of the following material:                carbonized paper produced by winding a capacitor element using so-called separator and then carbonizing the separator by heating or the like;        a material mainly containing non-woven fabric of glass fiber; or        a material mainly containing non-woven fabric of synthetic fiber such as vinylon, polyester, or polyamide.Here, the separator is made of Manila hemp or kraft paper that is used in a conventional electrolytic capacitor employing electrolyte for driving as the electrolyte.        
As the polymer molecule employed in the solid electrolyte, the following materials are known:                poly-(3,4-ethylenedioxythiophene) (hereinafter referred to as “PEDT”) produced by chemically oxidatively polymerizing 3,4-ethylenedioxythiophene (hereinafter referred to as “EDT”) with ferric p-toluenesulfonate; and        polypyrrole (hereinafter referred to as “PPY”) produced by chemically oxidatively polymerizing pyrrole monomer with ferric chloride or persulfate.        
While, a winding electrolytic capacitor employing both solid electrolyte made of conductive polymer molecule and electrolyte for driving as the cathode material is proposed.
In examples of the winding electrolytic capacitor, one of the group of separator paper such as Manila paper or kraft paper, porous film, and non-woven fabric separator of synthetic fiber is to be electric conductive with conductive polymer molecules that are chemically oxidatively polymerized with persulfate, and this electric conductive separator and electrolyte for driving are used. These examples are disclosed in Japanese Patent No. 2571941 and Japanese Patent Unexamined Publication No. H7-249543. An electrolytic capacitor where conductive polymer and electrolyte for driving are impregnated into a winding capacitor element is disclosed in Japanese Patent Unexamined Publication No. H11-186110.
In the winding SEC, however, a capacitor element is formed by winding anode foil having dielectric oxide film and etched cathode foil while disposing a separator between them, and the conductive polymer molecules forming the electrolyte are formed by dipping the capacitor element into solution for polymerizing and chemically oxidatively polymerizing it. As a result, as the size of the capacitor element is increased, solution for polymerization becomes less in the longitudinal central part of the capacitor element. Therefore, disadvantageously, the formed conductive polymer molecules become inhomogeneous, conductivity is decreased, and the ESR characteristic in a high frequency region is not improved.
For improving the impregnating ability of the solution for polymerizing into the capacitor element, it is effective to reduce the density of the separator.
When the Manila paper or kraft paper is used, however, the strength of the separator itself decreases to degrade short circuiting rate in winding.
Even when non-woven fabric of synthetic fiber capable of keeping the strength of the separator itself is used, basis weight decreases when the thickness of the non-woven fabric is made uniform and the density is decreased. Therefore, disadvantageously, the rate of occurrence of the short-circuit increases during aging in a manufacturing process of the capacitor, and the manufacturing rejection rate is extremely higher than that of the electrolytic capacitor using only the electrolyte for driving.
For improving the problems, an electrolytic capacitor employing both solid electrolyte made of conductive polymer molecules and electrolyte for driving as the cathode material is proposed. However, the electrolytic capacitor is composed of the conductive polymer molecules formed by performing chemical oxidative polymerization using persulfate such as sodium persulfate or ammonium persulfate, namely inorganic acid, as an oxidizing agent and dopant agent, so that the persulfate ions functioning as the dopant de-dope easily.
The persulfate ions are easily eluted into the electrolyte for driving, or the de-doping extremely reduces the conductivity of the conductive polymer molecules. Therefore, disadvantageously, thermal stability is low in the produced electrolytic capacitor, and the change over time of the ESR in the high frequency region is large.
The present invention addresses the conventional problems. The present invention provides a conductive separator that has high conductivity, is stable for the electrolyte for driving, and can realize an electrolytic capacitor having low ESR, and provides an electrolytic capacitor employing the conductive separator.